Technical field
The embodiments herein generally relate to the field of tissue engineering. The embodiments herein particularly relate to fabrication of scaffolds for skin tissue regeneration. The embodiments herein more particularly relate to fabrication of fiber reinforced hydrogel scaffold for skin tissue engineering.
Description of the Related Art
Wounds are defined as disruption of any tissue or cellular integrity due to mechanical, physical or metabolism (mainly due to diabetes mellitus) related injuries. In response to the injury or as a recovery or healing process, the major priority is to stop hemorrhage, to avoid excessive blood loss, and prevent microbial infection by infiltration of immune cells, such as neutrophils or macrophages. More importantly, it is critical to restore the function of the damaged tissue or cell through rapid healing. Wound healing is a stepwise process which includes (1) an inflammatory stage characterized by macrophage or leucocytes infiltration and cytokine production; (2) a proliferative phase which includes removal of damaged tissue and formation of granulation tissue in the wound; (3) a maturation phase wherein extracellular matrix produced by the proliferative tissue becomes well-defined; and (4) the formation of scar tissue indicating the completion of the wound healing process. The process of wound healing is more or less similar in all types of tissues, including skin tissue. In particular, skin tissue wounds are categorized as epidermal, dermal or dermo-epidermal, based on the degree and intensity of such wounds. The molecular mechanism of skin wound healing mainly involves production of various growth factors, such as epidermal growth factors (EGF) and tissue growth factors alpha and beta (TGF-α, TGF-β), etc. The conventional approaches used for instant healing of skin wounds include the use of natural products that have anti-inflammatory, anti-microbial and antioxidant properties, such as turmeric (active component curcumin), honey, etc. Hot or cold fomentation at the wound site may reduce inflammation and fasten the healing process.
In the recent few years, the field of regenerative tissue engineering has emerged as a gold standard platform for the development of artificial tissues and organ regeneration, to resolve major health related issues in humans. Multiple disciplines, such as cell biology, biomaterial research, bioengineering, etc., have contributed to the flourishing advances of tissue engineering. The major principle of tissue engineering is to restore and improve the function of the tissues by either generating novel or biocompatible substitutes or by reconstruction of the tissues. Use of cells or cell implants, delivery of tissue growth enhancing factors and use of various matrices, such as scaffolds to generate three dimensional (3D) cellular structures are the three major pioneering approaches of tissue regenerative medicine.
Over the past several years, skin tissue regeneration has shown promise due to the invention of several novel skin tissue engineered products. A plurality of (allograft, autograft, xenograft) grafts of dermal, epidermal or dermo-epidermal origin have been reported and have been used commercially. Such grafts help restore the structure of the skin tissue by repairing the wound effectively.
Such bioengineered skin substitutes not only repair the wounds, but also have various supplements, such as growth factors, antibiotics and anti-inflammatory drugs which eventually fasten the wound healing process. To engineer these substitutes, various scaffold matrices have been developed to promote cell growth in 3D structure. Such scaffolds are highly biocompatible with skin tissue and biodegradable in nature, acting as suitable dressing material for wound healing. Recent advances in the skin tissue engineering field revolve around the use of scaffolds with cell population, such as keratinocytes and fibroblasts.
A biomaterial is a material that is fabricated to interact with biological systems. Biomaterials can take many forms including a homogenous material, a blended material, or composite material. Often such biomaterials are designed to have usefulness in the medical field for diagnostic as well as therapeutic purposes. Biomaterials can be fabricated from natural as well as synthetic materials. Biomaterials can include polymers, metals, ceramics, and many other materials.
A plurality of scaffolds are fabricated for tissue regeneration and tissue engineering. These scaffolds provide a template on which cells can migrate, divide, secrete new matrix and differentiate. Typical tissue engineering scaffolds are porous and are categorized as having pores on either a micrometer scale, i.e. microporous, or a nanometer scale, i.e. nanoporous. Scaffolds having pores on a micrometer scale, or having average pore diameter of about 10 to 1000 microns, are composed of a variety of biocompatible materials including metals, ceramics and polymers. Such scaffolds include solid-cast structures, open-pore foams, felts, meshes, nonwovens, woven and knitted constructs. The mechanical and conformational properties are chosen by composition of the material and the design of the scaffold. The desirable mechanical properties include the ability to be sutured in place and good handling strength.
Composition, design and construction of the scaffold are also important to how tissue responds to the scaffold. The scaffold is shaped to maximize surface area, to allow adequate diffusion of nutrients and growth factors to cells present in or growing into it. A scaffold must be configured with pores on a micrometer scale. The pores provide enhanced surface area for the cells to be nourished by diffusion until new blood vessels interdigitate the implanted scaffold.
The scaffolds having pores on a nanometer scale, e.g. having average pore diameter of about 10 nanometers to 1 micron, are often composed of hydrogels. A hydrogel is a substance formed when a natural or synthetic organic polymer is cross-linked via covalent, ionic or hydrogen bonds to create a three-dimensional open-lattice structure, which entraps water molecules and forms a gel. Examples of materials that can be used to form a hydrogel include polyamides, methylcellulose, collagen, extracellular matrix (ECM), polysaccharides such as alginate, polyphosphazines, polyacrylates which are crosslinked tonically, high molecular weight poly (oxyalkylene ether), nonionic polymerized alkylene oxide compounds, or polyethylene oxide-polypropylene glycol block copolymers.
Hydrogels provide conformable, malleable, or injectable materials for administering cells into a tissue. They do not, however, have mechanical integrity. Synthetic hydrogels are sterilized and do not have the risk of associated infectious agents. However, most synthetic hydrogels do not mimic the extracellular matrix and therefore do not direct cellular ingrowth or function. Hydrogels of natural extracellular matrix are biocompatible and can mimic the native cellular environment. However, natural hydrogels, unless made from autologous material, may elicit an immune response and may have associated infectious agents. Natural hydrogels, such as EHS mouse sarcoma basement membrane, or fibrin, have a fiber diameter of about 5 to about 10 nanometers, water content of about 80 to about 97 wt % and average pore diameter of about 50 to about 400 nm.
Among the recent technologies in the multidisciplinary field of tissue engineering or regenerative medicine, use of various types of scaffolds is the key component. In tissue engineering, scaffolds are the best materials for restoring, maintaining and improving tissue function. They play a unique role in repair and more importantly regeneration of tissues by providing a suitable platform, permitting essential supply of various factors associated with survival, proliferation and differentiation of cells. Scaffolds can be made up of synthetic or absorbable, naturally occurring, biological, degradable or non-degradable polymeric materials. Several techniques have been used to construct scaffolds but the four major scaffolding approaches include the use of ECM secreting cell sheets, pre-made porous scaffolds of synthetic, natural and biodegradable biomaterials, decellularized ECM scaffolds, and cells entrapped in hydrogels. All these approaches have advantages as well as drawbacks. In this review, we intend to focus on the different types of scaffolds based on their biomaterial design and their advantages/disadvantages, especially those scaffolds which are extensively used for skin tissue regeneration.
The biomaterials are either natural or synthetic or a combination of both (composite scaffolds). Due to their resemblance to the natural extracellular matrix (ECM), biocompatibility, and biodegradability, natural polymers are widely used in wound and burn dressing. Natural polymers used in skin regeneration are of protein or carbohydrate origin. These polymers stimulate the healing by repair of the damaged tissue and promote effective skin regeneration. The synthetic polymers are fabricated mainly using electrospinning with controlled degradation characteristics and architecture.
Hyaluronic acid (HA) is a natural, non-sulfated glycosaminoglycan that plays an important role in skin morphogenesis and wound repair. HA and its derivatives have been widely used as hydrogels for tissue engineering due to its inherent biocompatibility and biodegradability characteristics, as well as their gel-forming properties. Using HA as a skin tissue engineering material could provide key advantages because it has been known to promote elastin secretion in valvular interstitial cells. Furthermore, HA can be methacrylated (HAMA) and thus can be rendered photocrosslinkable upon UV exposure. However, HA alone does not promote cell spreading; thus, combining HAMA and methacrylated gelatin (GelMA) could provide a more suitable microenvironment for the cells. However, these hydrogels lack the structural integrity necessary for skin formation. The mechanical shortcomings of the hydrogel structure can be addressed by adding a microfibrous component to reinforce the structure and to provide contact guidance, which is essential for directing the internal organization of the cells.
The fibrous scaffolds can be produced by electrospinning, resulting in a highly porous structure that retains desirable mechanical properties such that it can accommodate directional tensile loads while maintaining mechanical flexibility. However, the high porosity of the PGS-PCL microfibrous scaffolds allows seeded cells to migrate out of the structure. Furthermore, cells tend to attach only on the surface of the scaffold, which makes producing fully cellularized 3D structures difficult.
Hence there is a need to fabricate a composite biomaterial which combines extracellular matrix (ECM) mimicking hydrogels and elastomeric and elastomers poly (glycerol sebacate)-poly (ε-caprolactone) (PGS-PCL) electrospun (ES) scaffolds to mimic the cellular environment and mechanical properties of the native skin tissue. Also, there is a need for a hydrogel composite scaffold for retaining cells within the composite structures, while PGS-PCL component provides mechanical strength and a porous structure to support tissue growth.
The above-mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.